Apple on Wednesday released the AirPods software update version 3.7.2, bringing unspecified improvements and bug fixes to its Bluetooth earbuds featuring the in-house designed W1 wireless chip. According to German-language publication Macerkopf.de (Google Translate), it's possible that the new firmware addresses the reported connections issues where AirPods would lost iPhone connection during phone calls.
To install the new AirPods firmware, put both earbuds inside their charging case, then close the case and connect it to a charger or a USB port on your computer. Your iPhone must be paired with your AirPods and connected to Wi-Fi in order for the firmware to download and install.
TUTORIAL: How to install software updates for your AirPods
Updating AirPods firmware may take a few minutes to complete.
During the update process, your AirPods may be unavailable for use.
You can find out your AirPods firmware version in Settings → General → About → AirPods on your iPhone (your earbuds must be connected to the phone).
AirPods originally released with firmware version 3.3.1.